AMD's Gen2 PCIe, is it really a limitation?

cybrnook

cybrnook

[H]ard|Gawd
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Since 990fx is the last chip set seemingly being released for the AM3+ processors (also no more being released). I still feel that the platform as a whole is more than enough for todays workloads. In regards to today's uber picky and knowledgeable PC gaming community, with us moving into 4096 bit memory bus's (390x), do we think that we will see the point where gen 2 PCIe will be saturated and the need for Gen3 will render the 990fx platform a non contender? Or is it STILL working fine even with today's higher res expectations? Thoughts?

Or will there be a shift to gen 4?
 
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Only on the highest end cards with 8x PCI-E lanes. It's still not a bottleneck for any mid-range (think 280x/7970/GTX 680/770 level cards) or lower, especially at 1080p resolutions.
 
I had an overclocked GTX 980 Matrix in my AM3+ board and still got an average of 80+ FPS on Watch Dogs maxed out with SMAA on. I don't think PCI-E 2.0 was holding it back by any huge margin.
 
It's more of an issue for GPU compute workloads where there's more back and forth between main memory and the gpu memory. In games the workload is mostly one way. Load stuff to the gpu then the gpu works on stuff in it's memory.
 
So, let's talk about stress points as far as PCIe slot is concerned.

Where would the pain points be felt more, PCIe GEN 3 at 8x or PCIe GEN 2 at 16x, and what brings the limitations into play, textures, resolutions? I would think more the latter, the higher the res, the more data is traversing the bus exposing the bottleneck quicker.
 
Sure, I read that thanks. But my questions are asked in two different ways not just GEN 3 x 8, but also towards GEN 2 x 16.

Guess I just posted in the dead AMD section :), should have posted mine in the general area I guess a month ago :)
 
That review has both Gen 2 and 3 with performance vs a lot of games with practically every level of PCIe bus lanes/generation. I suppose I don't understand the question.

Gen 2 x16 does start limiting the 980 in some games. It'll only get worse going forward.
 
Thanks for shaking me a bit there. I was able to find the quotes I was looking for in W1zz's article:

"For the majority of games, there is no significant performance difference between x16 3.0 and x8 3.0 (and x16 2.0, which offers the same bandwidth). The average difference is only 1%, which you'd never notice. Even such bandwidth-restricted scenario as x16 1.1 or x8 2.0, offered by seriously old motherboards, only saw a small difference of around 5%. The same goes for x4 3.0, which is the bandwidth offered by the x4 slots on some recent motherboards. It's worth noting here that not all x4 slots are wired to the CPU. Some of the cheaper motherboards have their PCIe x16 (electrical x4) slots wired to the chipset instead of the CPU, which could severely clog the chipset bus (the connection between the CPU and the chipset, limited to a mere 2 GB/s on the Intel platform). Refer to the block-diagram in your motherboard's manual.

Real performance losses only become apparent in x8 1.1 and x4 2.0, where the performance drop becomes noticeable with around 15%. We also tested x4 1.1, though of more academic interest, and saw performance drop by up to 25%, an indicator that PCIe bandwidth can't be constrained indefinitely without a serious loss in performance."
 
related question(s)...

1) The 990FX apparently only has 32 lanes of PCIE 2.0... So if I ran 2 x16 lanes for crossfire, would that prevent me from using any other PCIE cards like an SSD?

2) Are there any reviews on PCIE 2.0 x8 bottlenecks? I'm looking at 290xs...
 
Yeah, now you have me thinking if my 750ti (for Physx) is gimping my Titan X SLI. I wonder if that card will work in a 4x slot so my Titan X's will be at 16x instead of this 16x 8x 8x crap. I googled it and it looks like there's no way to manually change it in BIOs...

I wish they took frametimes on one of the worse performers like Ryse to see how the bottle necking manifests itself.
 
The exact reason I only have 2 x cards on my MB. With my board I get 2 x 16 SLI. However, even if I was to plug in a sound card, it would drop down to x8 x8 (or 16 x 8). I have 3 970's laying around at my house, so trust me, I thought of dedicated Physics. But I stayed away from it.

However to the earlier argument. We technically should NOT be affect at GEN 3 x8 x8 (But placebo tells me otherwise).

:)

For the AMD question, this was a great read from W1zzard over at TPU, https://www.techpowerup.com/reviews/NVIDIA/GTX_980_PCI-Express_Scaling/
That's where I got my piece of mind as far as GEN2 vs GEN 3 x8 vs x16
 
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cybrnook said:
The exact reason I only have 2 x cards on my MB. With my board I get 2 x 16 SLI. However, even if I was to plug in a sound card, it would drop down to x8 x8 (or 16 x 8). I have 3 970's laying around at my house, so trust me, I thought of dedicated Physics. But I stayed away from it.

However to the earlier argument. We technically should NOT be affect at GEN 3 x8 x8 (But placebo tells me otherwise).

:)

For the AMD question, this was a great read from W1zzard over at TPU, GeForce GTX 980 PCI-Express Scaling
That's where I got my piece of mind as far as GEN2 vs GEN 3 x8 vs x16
Click to expand...

What board do you have?

I have a 990fx board coming (ASUS M5A99FX Pro 2.0) and it has 2 x16 slots that the lanes are not shared with the other slots from what I understand. The other 2 x16 slots are x4 electrically, plus there is another x1 slot besides.

No worries on the PCIe 2.0 as I will only be using it for a pair of HD6870 cards for a "retro" xp machine.
 
I just read an article a few days ago on hardwaresecrets that does some comparison on Gen 2 & Gen 3 slots. Basically there is no difference. I think 1 game made a slight difference. Which means like when you own SLI there is 1 game that doesn't work right and the rest do. I'm a noob so I can't post the link, but it is on the front page...fyi
 
DrLobotomy said:
I just read an article a few days ago on hardwaresecrets that does some comparison on Gen 2 & Gen 3 slots. Basically there is no difference. I think 1 game made a slight difference. Which means like when you own SLI there is 1 game that doesn't work right and the rest do. I'm a noob so I can't post the link, but it is on the front page...fyi
Click to expand...

Keep in mind that Intel's PCI-E slots go directly to the CPU, while AMD's go to the northbridge, then the CPU through the HT link. The northbridge/HT link can be a bottleneck in certain games, especially games that transfer a lot of data to the GPUs. FM2+ does not have a northbridge like Intel, but I haven't seen any reputable multi-GPU tests on the FM2+ platform.
 
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